This middleware catches exceptions (run-time errors) happening in your application and displays nice stack trace screen. The stack trace is also stored in the environment as a plaintext and HTML under the key plack.stacktrace.text and plack.stacktrace.html respectively, so that middleware futher up the stack can reference it.

This middleware is enabled by default when you run plackup in the default development mode.

You're recommended to use this middleware during the development and use Plack::Middleware::HTTPExceptions in the deployment mode as a replacement, so that all the exceptions thrown from your application still get caught and rendered as a 500 error response, rather than crashing the web server.

Force display the stack trace when an error occurs within your application and the response code from your application is 500. Defaults to off.

The use case of this option is that when your framework catches all the exceptions in the main handler and returns all failures in your code as a normal 500 PSGI error response. In such cases, this middleware would never have a chance to display errors because it can't tell if it's an application error or just random eval in your code. This option enforces the middleware to display stack trace even if it's not the direct error thrown by the application.